Phase transition and dielectric study in Ba<Subscript>0·95</Subscript>Dy<Subscript>0·05</Subscript>TiO<Subscript>3</Subscript> ceramic

Temperature and frequency dependence dielectric permittivity of Ba0·95Dy0·05TiO₃ ceramic has been studied in the temperature range of 100–350 K at the frequencies, 1 kHz, 10 kHz, 100 kHz and 1 mHz. Diffuse phase transition and frequency dispersion is observed in the permittivity-vs-temperature plots. This has been attributed to the occurrence of relaxor ferroelectric behaviour. The observed relaxor behaviour has been quantitatively characterized based on phenomenological parameters. A comparison with the Zr doped BaTiO₃ has also been presented. The microstructure of as-sintered samples shows a dense and almost uniform micrograph without any impurity phases; the grains are almost spherical with random orientation.     

Investigation of density of states and electrical properties of Ba<Subscript>0.5</Subscript>Co<Subscript>0.5</Subscript>Bi<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> nanoceramics prepared by chemical route

Barium-cobalt-bismuth-niobate, Ba_0.5Co_0.5Bi₂Nb₂O₉ (BCoBN) nanocrystalline ferroelectric ceramic was prepared through chemical route. XRD analysis showed single phase layered perovskite structure of BCoBN when calcined at 650 °C, 2 h. The average crystallite size was found to be 18 nm. The microstructure was studied through scanning electron microscopy. The dielectric and ferroelectric properties were investigated in the temperature range 50–500 °C. The dielectric constant and dielectric loss plot with respect to temperature both indicated strong relaxor behavior. Frequency versus complex impedance plot also supported the relaxor properties of the material. The impedance spectroscopy study showed only grain conductivity. Variation of ac conductivity study exhibited Arrhenius type of electrical conductivity where the hopping frequency shifted towards higher frequency region with increasing temperature. The ac conductivity values were used to evaluate the density of state at the Fermi level. The minimum hopping distance was found to be decreased with increasing temperature.     

Relaxor behavior and ferroelectric properties of Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-K<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-KNbO<Subscript>3</Subscript> lead-free ceramics

Lead-free ferroelectric ceramics of (1−x) [0.88Na_0.5Bi_0.5TiO₃-0.12K_0.5Bi_0.5TiO₃]-x KNbO₃(x = 0, 0.02, 0.04, and 0.06) were prepared by the conventional ceramic fabrication technique. The crystal structure, dielectric properties and P-E hysteresis loops were investigated. XRD data showed that all compositions could form pure perovskite structure. Temperature dependence of dielectric constant ε _r and dissipation factor tanδ measurement between room temperature and 500^∘C revealed that the compounds experience phase transitions that from ferroelectric to anti-ferroelectric and anti-ferroelectric to paraelectric in the range of x = 0–0.04. The frequency dependent dielectric constant showed these compounds were relaxor ferroelectric. At low frequency and high temperature, dielectric constant and dissipation factor increased sharply attributed to the superparaelectric clusters after the KNbO₃ doped.     

Study on dielectric and tunable properties of Cr-doped Ba<Subscript>0</Subscript><Subscript>.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> thin films by rf sputtering

Ba_0.6Sr_0.4TiO₃ dielectric thin films doped by Cr(0, 1, 2.5, 5, 10 mol%) (BSTC) were prepared by radio frequency magnetron sputtering on Pt/Ti/SiO₂/Si substrates. The structure and morphology of the BSTC thin films were studied by atomic force microscopy and X-ray diffraction. The effect of Cr doping on the dielectric properties of BST thin films were analyzed. The results show that the dielectric loss of Cr doping BST thin films is lower than that undoped, and the tunability increased with Cr doping. The thin film doped with 5 mol% Cr has the best dielectric properties. The tunability, loss and figure of merit (FOM) at 1 MHz were 38.9%, 0.0183, and 21.3, respectively.     

Strain-induced artificial multiferroicity in Pb(Zr<Subscript>0.53</Subscript>Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript>/Pb(Fe<Subscript>0.66</Subscript>W<Subscript>0.33</Subscript>)O<Subscript>3</Subscript> layered nanostructure at ambient temperature

Layered nanostructures (LNs) of the commercial ferroelectric Pb(Zr_0.53Ti_0.47)O₃ (PZT) and the natural ferroic relaxor Pb(Fe_0.66W_0.33)O₃ (PFW) were fabricated with a periodicity of PZT/PFW/PZT (~5/1/5 nm, thickness ~250 nm) on MgO substrates by pulsed laser deposition. The dielectric behavior of these LNs were investigated over a wide range of temperatures and frequencies, observing Debye-type relaxation with marked deviation at elevated temperatures (>400 K). High dielectric constant and very low dielectric loss were observed below 100 kHz and 400 K, whereas the dielectric constant decreases and loss increases with increase in frequency, similar to relaxor ferroelectrics. Asymmetric ferroelectric hysteresis loops across UP and DOWN electric field were observed with high remanent polarization (P_r) of about 33 μC/cm². High imprint (~5–7 V across 250 nm thin films) were seen in ferroelectric hysteresis that may be due to charge accumulation at the interface of layers or significant amount of strain (~3.21) across the layers. Room temperature ferromagnetic hysteresis was observed with remanent magnetization 5.32 emu/cc and a coercive field of ~550 Oe. Temperature and field dependent leakage current densities showed very low leakage ~10⁻⁷–10⁻⁵ A/cm² over 500 kV/cm. We observed imprint in hysteresis that may be due to charge accumulation at the interface of layers or active role of polar nano regions (PNRs) situated in the PFW regions.     

The effects of CuO-doping on dielectric and piezoelectric properties of Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–Ba(Zr,Ti)O<Subscript>3</Subscript> lead-free ceramics

CuO-doped lead-free ceramics based on bismuth sodium titanate (Bi_0.5Na_0.5TiO₃, BNT) and barium zirconate titanate (Ba(Zr_0.07Ti_0.93)O₃, BZT) were prepared via a multi-step solid-state reaction process. The BNT–BZT with CuO dopant ceramics sintered at 1150–1180 °C for 2 h in air showed a pure perovskite structure. SEM images reveal that a small amount of CuO (<2 mol%) play a significant role on the microstructure to improve its sintering attributes, while it will degrade when the dopant is added beyond 2 mol%. The dielectric and piezoelectric properties of CuO-doped BNT–BZT ceramics were evaluated. At room temperature, the sample doped with 2 mol% CuO shows quite good properties such as a high piezoelectric constant (d ₃₃ ∼156.5 pC/N) and a high electromechanical coupling factor (k _t ∼52%). The depolarization temperature increased dramatically and the maximum permittivity temperature decreased slightly.     

Dielectric properties and relaxation of Bi<Subscript>0·5</Subscript>Na<Subscript>0·5</Subscript>TiO<Subscript>3</Subscript>-BaNb<Subscript>2</Subscript>O<Subscript>6</Subscript> lead-free ceramics

A new member of lead-free piezoelectric ceramics of the BNT-based group, (1 − x)Bi_0·5Na_0·5TiO_3−x BaNb₂O₆, was prepared by conventional solid state reaction and its dielectric properties and relaxation was investigated. X-ray diffraction showed that BaNb2O6 diffused into the lattice of Bi_0·5Na_0·5TiO₃ to form a solid solution with perovskite-type structure. A diffuse character was proved by the linear fitting of the modified Curie-Weiss law. The temperature dependence of dielectric constant at different frequencies revealed that the solid solution exhibited relaxor characteristics different from classic relaxor ferroelectrics. The samples with x = 0·002 and 0·006 exhibited obvious relaxor characteristics near the low temperature dielectric abnormal peak, T _f, and the samples with x = 0·010 and 0·014 exhibited obvious relaxor characteristics between room temperature and T _f. The mechanism of relaxor behaviour was also discussed according to the macro-domain to micro-domain transition theory.     

Dielectric and ferromagnetic properties of BaTiO<Subscript>3</Subscript>/Ni<Subscript>0.93</Subscript>Co<Subscript>0.02</Subscript>Cu<Subscript>0.05</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> composites

xBaTiO₃ + (1 − x)Ni_0.93Co_0.02Cu_0.05Fe₂O₄ (x = 0.5, 0.6, 0.7, 0.8) composites with ferroelectric–ferromagnetic characteristics were synthesized by the ceramic sintering technique. The presence of constituent phases in the composites was confirmed by X-ray diffraction studies. The average grain size was calculated by using a scanning electron micrograph. The dielectric characteristics were studied in the 100 kHz to 15 MHz. The dielectric constant changed higher with ferroelectric content increasing; and it was constant in this frequency range. The relation of dielectric constant with temperature was researched at 1, 10, 100 kHz. The Curie temperature would be higher with frequency increasing. The hysteresis behavior was studied to understand the magnetic properties such as saturation magnetization (M _s). The composites were a typical soft magnetic character with low coercive force. Both the ferroelectric and ferromagnetic phases preserve their basic properties in the bulk composite, thus these composites are good candidates as magnetoelectric materials.     

Structural and dielectric properties of PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>-PbZrO<Subscript>3</Subscript> solid solutions synthesized at high pressures and temperatures

(1 ? x)PbMg_1/3Nb_2/3O₃ · xPbZrO₃ (1 ? x)PMN · xPZ) solid solutions have been synthesized at a pressure of 5 GPa and temperatures from 1300 to 1700 K, and their structural and dielectric properties have been studied. The composition dependences of the average unit-cell parameter and dielectric permittivity for the solid solutions indicate that the PMN-PZ system has a morphotropic phase boundary near x = 0.65. The solid solutions have a cubic structure for x < 0.65, a rhombohedral structure in the range 0.65 < x < 0.9, and an orthorhombic structure (similar to that of PbZrO₃) for x > 0.9. The temperature and frequency dependences of dielectric permittivity suggest that the (1 ? x)PMN · xPZ samples with x < 0.65 consist of two ferroelectric phases: a relaxor with antipolar dipole order and a normal ferroelectric with a diffuse phase transition. The effect of annealing temperature on the ferroelectric state of the samples with x < 0.65 is examined. In the composition range 0.65 < x < 0.9, the samples have normal ferroelectric properties, independent of annealing temperature.     

Effect of CeO<Subscript>2</Subscript> on dielectric,ferroelectric and piezoelectric properties of PMN–PT (67/33) compositions

Lead magnesium niobate–lead titanate [Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃] powders doped with different mole % of CeO₂ were prepared by a modified columbite route with compositions corresponding to morphotropic phase boundary (MPB) region. These powders were calcined at 800 °C for 4 h and circular test specimens were prepared by uniaxial pressing. The specimens were sintered at 1150 °C/2 h, poled at 2 kV/mm d.c. voltage and were characterized for dielectric, ferroelectric and piezoelectric properties. It was observed that the piezoelectric and ferroelectric properties initially increase up to 2 mol% of ceria addition and then decrease with increase in ceria concentration. The diffusivity of the dielectric curves increases with increase in ceria concentration. The decrease in Curie temperature was observed from 173 °C corresponding to pure PMN–PT to a temperature of 138 °C for 10 mol% of ceria addition.     

Dielectric and a.c. conductivity studies in pure and manganese doped layered K<Subscript>2</Subscript>Ti<Subscript>4</Subscript>O<Subscript>9</Subscript> ceramics

The results of a.c. electrical conductivity studies have been reported on pure K₂Ti₄O₉ (named PT) and its 1.0 molar percentage of MnO₂ doped derivative (named MPT) ceramics in the temperature range 373–898 K. Four regions have been identified in the log(σ_a.c. T) versus 1000/T plots. Conduction in the lowest temperature region I is attributed to the mixed exchangeable interlayer ionic and electronic hopping (polaron) conduction. A dielectric loss peak with distribution of relaxation times perturbs the conduction in next regions II and III. However, in region III for both the samples non-relaxor ferroelectric property may be proposed. The modified interlayer ionic conduction has been proposed towards the higher temperature region IV. Loss tangent (tan δ) versus frequency and dielectric constant (ε) versus frequency plots at different temperatures have also been given for both the samples. The results of tan δ versus temperature and ε versus temperature at different frequencies have further been reported for both of the above compounds in this paper.     

Structural and electric properties of (Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>)<Subscript>0.88</Subscript>Ba<Subscript>0.12</Subscript>TiO<Subscript>3</Subscript>

Lead-free (Na_0.5Bi_0.5)_0.88Ba_0.12TiO₃ ceramics have been prepared and studied by X-ray diffraction and by the complex dielectric response as a function of temperature, frequency and a.c. field intensity. Relaxor-like dielectric behaviour were induced by barium Ba dopping to Na_0.5Bi_0.5TiO₃. It was shown, that relaxor-like characteristics can be enhanced by the increase of the a.c. field intensity. A sharp increase in the electric permittivity and dielectric loss on heating near 230 °C has been observed. This sharp increase in dielectric responses indicates a transformation between classical and relaxor ferroelectric phases. The X-ray diffraction study shows that this transformation corresponds to the first order phase transition from tetragonal to cubic. The use of (Na_0.5Bi_0.5)_0.88Ba_0.12TiO₃ ceramics for device applications has been indicated.     

Temperature-stable and low loss Fe-containing dielectrics in BaO-Ln<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> system

Polycrystalline samples of Ba₄Ln₂Fe₂Ta₈O₃₀ (Ln = La and Nd) were prepared by a high temperature solid-state reaction technique. The formation, structure, dielectric and ferroelectric properties of the compounds were studied. Both compounds are found to be paraelectrics with filled tetragonal tungsten bronze (TB) structure at room temperature. Dielectric measurements revealed that the present ceramics have exceptional temperature stability, a relatively small temperature coefficient of dielectric constant (τ _ε ) of −25 and −58 ppm/°C, with a high dielectric constant of 118 and 96 together with a low dielectric loss of 1.2 × 10⁻³ and 2.8 × 10⁻³ (at 1 MHz) for Ba₄La₂Fe₂Ta₈O₃₀ and Ba₄Nd₂Fe₂Ta₈O₃₀, respectively. The measured dielectric properties indicate that both materials are possible candidates for the fabrication of discrete multilayer capacitors in microelectronic technology.     

Synthesis and characterization of pseudo-ternary Pb(Fe<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>)O<Subscript>3</Subscript>-PbZrO<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> ferroelectric ceramics via a B-site oxide mixing route

Perovskite phase formation and dielectric/ferroelectric properties of the pseudo-ternary Pb(Fe_1/2Nb_1/2)O₃-PbZrO₃-PbTiO₃ (PFN-PZ-PT) ferroelectric ceramics have been investigated as promising materials for multi-layer ceramic capacitors. Complete solid solution with pure perovskite phase can be formed in this system in the whole composition range studied using conventional solid-state reaction method via a B-site oxide mixing route. Crystal lattice of the ceramics obtained shrinkages with the increase of the concentration of Pb(Fe_1/2Nb_1/2)O₃ (PFN) and expands with the increase of the content of PbZrO₃ (PZ). With the increase of the concentration of PbTiO₃ (PT), crystal structure of PFN-PZ-PT changes from pseudo-cubic ferroelectric phase to tetragonal one while retains the fraction of PFN as constant. A morphotropic phase boundary (MPB) forms at the composition of 42 mol% PT regardless of whatever concentration of PFN, and the content of PFN affects little on the composition of MPB. The preliminary phase diagram of the PFN-PZ-PT system is determined by X-ray diffraction (XRD) measurements combining with dielectric/ferroelectric characterization. Dielectric measurements indicate that the value of dielectric maximum (ɛ_m) and the temperature where ɛ_m appears (T_m) increase with the increase of the concentration of PT. However, PFN exhibits opposite effects, i.e., ɛ_m increases with the increase of the concentration of PFN accompanied by the decrease of T_m.     

Properties of neodymium-doped Ca<Subscript>0.15</Subscript>Sr<Subscript>1.85</Subscript>Bi<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>18</Subscript> ferroelectric ceramics

Bismuth-layered compound Ca_0.15Sr_1.85Bi_4−xNd_xTi₅O₁₈ (CSBNT, x = 0–0.25) ferroelectric ceramics samples were prepared by solid-state reaction method. The effects of Nd³⁺ doping on their ferroelectric and dielectric properties were investigated. The remnant polarization Pr of CSBNT ceramics increases at beginning then decreases with increasing of Nd³⁺ doping level, and a maximum Pr value of 9.6 μC/cm² at x = 0.05 was detected with a coercive field Ec = 80.2 kV/cm. Nd³⁺ dopant not only decreases the Curie temperature linearly, but also the dielectric constant (ε_r) and dielectric loss tangent (tan δ). The magnitudes of ε_r and tan δ at the frequency of 100 kHz are estimated to be 164 and 0.0083 at room temperature, respectively.     

Effect of Eu<Subscript>2</Subscript>O<Subscript>3</Subscript> doping on the crystallization behavior of BaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

We gave studied the crystallization behavior of 30BaO · 25Bi₂O₃ · 45B₂O₃ glasses doped with Eu₂O₃ to different levels. At a Eu₂O₃ content of 7 mol % or higher, the glasses undergo volume crystallization. The only precipitating phase is a solid solution between europium and bismuth oxides. With increasing europium concentration in the glass, the structure of the crystallites changes from cubic to rhombohedral. We have investigated the morphology, physicochemical properties, and luminescence spectra of the glasses and glass-ceramics.     

Effects of sintering temperature on the properties of Mn/Y codoped Ba<Subscript>0.67</Subscript>Sr<Subscript>0.33</Subscript>TiO<Subscript>3</Subscript> ceramics for tunable application

(Ba_0.67Sr_0.33)_1?3x/2Y _x Ti_1?y/2Mn _y O₃ [BST(Mn + Y), x = 0.006, y = 0.005] ceramics were fabricated by using citrate–nitrate combustion derived powder. Microstructure and dielectric properties of the BST(Mn + Y) ceramic samples were investigated within the sintering temperature ranged from 1220 to 1300 °C. Sintering temperature has a great influence on the microstructure and electrical properties of the ceramic samples. The dielectric properties, ferroelectric properties, and tunability are enhanced by optimizing sintering temperature. The relatively high tunability of 40 % (1.5 kV/mm DC field, 10 kHz) was obtained, and relatively low dielectric loss, <0.0052 (at 10 kHz, 20 °C) was acquired for BST(Mn + Y) samples sintered at 1275 °C for 3 h. Both the low dielectric loss and enhanced tunable properties of BST(Mn + Y) are useful for tunable devices application.     

Properties of Na<Subscript>0.875</Subscript>Li<Subscript>0.125</Subscript>NbO<Subscript>3</Subscript> ceramics

The structural, dielectric, and thermal properties of the Na_0.875Li_0.125NbO₃ solid solution doped with strontium and other elements have been studied in wide temperature and frequency ranges. The material has been shown to undergo a sequence of phase transitions accompanied by anomalies in its structural, dielectric, and thermal properties. The observed low-frequency dispersion of its dielectric permittivity is attributed to the effect of electrical conductivity.     

Dielectric properties of Yb<Subscript>2</Subscript>O<Subscript>3</Subscript>-doped barium strontium calcium titanate thick films for microwave device applications

(Ba_0.56Sr_0.34Ca_0.10)TiO₃ (BSCT) thick films doped with 0.1 mol% MnCO₃ and Yb₂O₃ (0.1–0.7 mol%) were fabricated by the screen-printing method on the alumina substrate. The structural and electrical properties as a function of Yb₂O₃ amount were investigated. All BSCT thick films showed the formation of a complete solid solution in a cubic perovskite polycrystalline structure. Average grain size of the specimen doped with 0.7 mol% Yb₂O₃ was about 2.7 μm. The thickness of all BSCT thick films was approximately 50–55 μm. The relative dielectric constant, dielectric loss, and tunability of the BSCT thick films doped with 0.3 mol% Yb₂O₃ were 2,966, 0.7, and 14.3%, respectively.     

Nanocrystalline PbIn<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>O<Subscript>3</Subscript> ceramics and its properties

A ferroelectric relaxor PbIn_0.5Nb_0.5O₃ (PIN) ceramics has been obtained using a modified ceramic technology, with the sintering stage preceded by compression and shear straining of the synthesized charge in Bridgman anvils. The dimensions of ceramic grains after this pretreatment are spread over a range from 100 to 1250 nm. A comparative investigation of the properties of PIN ceramics obtained using the standard and modified technology showed that the proposed mechanical action at the charge preparation stage can be used for controlled modification of the properties of ferroelectric ceramics.